CVE-2008-1673 in Linux
Summary
by MITRE
The asn1 implementation in (a) the Linux kernel 2.4 before 2.4.36.6 and 2.6 before 2.6.25.5, as used in the cifs and ip_nat_snmp_basic modules; and (b) the gxsnmp package; does not properly validate length values during decoding of ASN.1 BER data, which allows remote attackers to cause a denial of service (crash) or execute arbitrary code via (1) a length greater than the working buffer, which can lead to an unspecified overflow; (2) an oid length of zero, which can lead to an off-by-one error; or (3) an indefinite length for a primitive encoding.
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Analysis
by VulDB Data Team • 08/11/2019
The vulnerability identified as CVE-2008-1673 represents a critical flaw in ASN.1 Basic Encoding Rules (BER) implementation across multiple network protocols and kernel modules. This weakness affects both the Linux kernel versions 2.4.x before 2.4.36.6 and 2.6.x before 2.6.25.5, specifically within the cifs and ip_nat_snmp_basic modules, as well as the gxsnmp package. The core issue stems from inadequate validation of length parameters during ASN.1 BER data decoding processes, creating multiple attack vectors that can be exploited by remote adversaries to compromise system stability and potentially execute arbitrary code. The vulnerability is classified under CWE-129, which addresses improper validation of length parameters, and aligns with ATT&CK technique T1210 for exploiting known vulnerabilities in operating systems.
The technical implementation flaw manifests through three distinct attack vectors that exploit different aspects of ASN.1 BER parsing. The first vector involves supplying a length value that exceeds the allocated working buffer size, potentially causing memory corruption and unspecified buffer overflows that can result in system crashes or code execution. The second vector exploits an edge case where Object Identifier (OID) length values are set to zero, creating off-by-one errors that can lead to memory access violations and system instability. The third vector targets the handling of indefinite length encodings for primitive data types, which can cause parsing routines to behave unpredictably and potentially execute malicious code. These vulnerabilities demonstrate a fundamental lack of input validation and proper boundary checking in the ASN.1 parsing libraries used by the affected systems.
The operational impact of this vulnerability extends beyond simple denial of service conditions to encompass potential system compromise and unauthorized code execution. Remote attackers can leverage these flaws to crash network services, particularly those relying on SNMP protocols such as the CIFS module and IP NAT SNMP basic functionality. The exploitation of these vulnerabilities can result in complete system compromise, especially when the affected kernel modules are actively processing network traffic containing maliciously crafted ASN.1 data. Attackers can potentially escalate privileges through code execution exploits, making this vulnerability particularly dangerous in environments where network services are exposed to untrusted networks. The vulnerability affects systems running vulnerable kernel versions and SNMP-based applications, creating widespread exposure across enterprise and server environments.
Mitigation strategies for CVE-2008-1673 require immediate patching of affected kernel versions and SNMP implementations to address the ASN.1 BER parsing flaws. System administrators should implement network segmentation and access controls to limit exposure of vulnerable services to untrusted networks, while also monitoring for suspicious network traffic patterns that might indicate exploitation attempts. The recommended approach includes updating to kernel versions 2.4.36.6 and 2.6.25.5 or later, which contain the necessary fixes for ASN.1 length validation. Organizations should also consider disabling SNMP services when not required, implementing proper input validation at network boundaries, and conducting regular security assessments to identify other potential vulnerabilities in ASN.1 implementations. Network intrusion detection systems should be configured to monitor for patterns consistent with the exploitation attempts described in the vulnerability, providing early warning of potential attacks. The remediation process must also include thorough testing of patched systems to ensure that the updates do not introduce compatibility issues with existing network services and applications.